Accurate delineations of irrigated acreage are critical in the development of water-use estimates and in determining an accurate water budget for the hydrographic basins of the BARCAS study area. Currently, irrigated acreage is estimated routinely for only a few basins in the study area and these acreages are calculated and reported by township range section, quarter, and quarter-quarter. Satellite imagery from the Landsat Thematic Mapper (TM) platform was used to delineate irrigated acreage for the BARCAS study area on a field by field basis. Six hundred and forty-three fields were delineated by interpreting satellite data. The water source, irrigation system, crop type, and field activity were identified and verified through field reconnaissance. These data were integrated into the geodatabase and analyzed to develop reasonably accurate estimates of irrigated acreage for the 2000, 2002, and 2005 growing seasons by hydrographic area and sub-area. Estimated average annual potential evapotranspiration and average annual precipitation were incorporated into the geodatabase as ancillary data. Irrigated acreage in 2005 totaled nearly 32,000 acres ranging from less than 200 acres in Butte, Cave, Jakes, Long, and Tippett Valleys to 9,200 acres in Snake Valley. Cave, Irrigated acreage increased about 20 percent from 2000 to 2005, with Snake and White River Valleys experiencing the greatest increases. The source for about 80 percent of irrigation water applied during drier years is ground water pumped from wells. About 80 percent of irrigation water applied in 2005 was through sprinkler systems, and about 20 percent was through flood systems. Fields planted in alfalfa accounted for about 88 percent of the irrigated acreage.